1. Field of the Invention
The invention relates to optical devices. In particular, the invention relates to optical multiplexers.
2. Background of the Invention
A common type of optical multiplexer includes a plurality of waveguides that intersect one another so as to combine light signals traveling along a plurality of input waveguides onto a smaller number of output waveguides. Each waveguide intersection increases the angle at which light signals are incident on the side of the waveguide. This angle is called the propagation angle. If the propagation angle is increased far enough, the waveguides can fail to constrain the light signal.
The propagation angle that can be supported by a waveguide is often a function of the waveguide material. For instance, multi-mode silicon waveguides can support higher propagation angles than multi-mode silica waveguides. As a result, a multi-mode multiplexer having silicon waveguides will support propagation angles that are not supported by a multi-mode silica fiber. When the multiplexer is coupled with the optical fiber such that a light signal travels from the multiplexer to the optical fiber, the portion of a light signal having high propagation angles will be lost upon entering the optical fiber. Accordingly, the increase in propagation angles caused by the waveguide intersections can serve as a source of optical loss.
For the above, reasons there is a need for a multiplexer having a reduced optical loss.